The invention relates to a method of producing an optical fiber, having a core which has a noncircular cross-section, by using a double crucible. In the double crucible, the outflow opening of the inner crucible is wholly within the space enclosed by the outer crucible.
Optical fibers of this nature can be used when it is necessary to suppress coupling between modes having different polarization directions. This is desirable when the pulse dispersion in a monomode fiber is reduced by compensation of material dispersion to such an extent that the chromatic dispersion amounts to some picosecs/km. nm. In order to maintain this level, it is desirable that the fiber propagates a polarized signal. Decoupling can be optimized if the fibers having the desired geometry are in a noncircular stress condition. (UK patent application No. GB 20 12 983).
Fibers of the type described above may be used as monomode telecommunication fibers. They may also be used as sensors, for example, in the measurement of a magnetic field, or more generally may be used in devices for measuring physical effects which produce mechanical stress in optical fibers.
The invention also relates to a double crucible suitable for manufacturing optical fibers having cores with noncircular cross-sections. The double crucible includes an inner crucible for the core glass material and an outer crucible for the cladding glass.
Optical fibers consisting of a light-conducting core having a noncircular, for example elliptical, cross-section are known per se. In these known fibers, the cladding directly contacts the core, and the shape of the cross-section of the fiber corresponds in general with the cross-section of the core. A fiber having a core which has an elliptical cross-section may itself have an elliptical cross-section (see, for example, U.S. Pat. No. 4,106,847).